I have a cylindrical power of 2.5 in 2014. Now it was 3. Why it get increased? Will it be a problem?

Not a problem. Changes in refraction error are common, and going from 2.5 to 3 diopters of cylinder correction (for astigmatism) does not suggest anything more serious. .
Vision. AS the lens changes its shape or size there can be change in vision resulting i change in power .